ftrace: Introduce and use ENTRIES_PER_PAGE_GROUP macro

ftrace: Introduce and use ENTRIES_PER_PAGE_GROUP macro

ENTRIES_PER_PAGE_GROUP() returns the number of dyn_ftrace entries in a page
group, identified by its order.

No functional change.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260113152243.3557219-2-linux@roeck-us.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>